For technological development, the determination of an element profile in a material (e.g. Nitrogen profile in a SiO2 layer, in High-K) is of major importance.
A number of techniques are known which may be helpful in obtaining such a profile.
Secondary Ion Mass Spectroscopy (SIMS) gives some insight into nitrogen concentration distribution. This approach has the disadvantage however of being suitable only for off-line use, and is furthermore time-consuming preventing fast and extensive investigation. Still further, the SIMS technique is subject to measurement uncertainties due to the surface of the Cesium analysis beam, the induced crater during sputtering, and matrix effects, as described for example in S. Wolf, R. N. Tauber, “Silicon Processing for the VLSI Era”, Lattice Press: Sunset Beach, Calif., 1986, Volume 1, Process Technology, p. 607.
Nuclear characterization techniques, such as Nuclear Reaction Analysis (NRA) and Medium Energy Ion Scattering (MEIS), give some meaningful information on the material properties, such as absolute quantification of the elements for NRA, element ratios through the film, and multi-layer inter-diffusion for MEIS. However, these techniques are not available inline. Facilities are costly and scarce, and usually require a lot of time to perform and analyze.
Auger depth profiling is similarly time-consuming and solely available off-line.
Generally, these solutions are time consuming, require an expert skilled in the art of performing these analysis, are costly, and time-consuming.
Also, these techniques are destructive and always performed off-line (out of the cleanroom).
Some in-line tools can give some information on the nitrogen profile. For example, the X-ray Photoelectron Spectroscopy (XPS) in-line tool allows measurements of SiON films, and provides access to the nitrogen dose and to its chemical bonding at the surface.
Primarily used as a fullsheet surface measurement technique, X-ray Photoelectron Spectroscopy (XPS) applications can be extended to element profile investigation using specific sample preparations that induce a bevel via wet etching of the films. The most advanced developments of this technique, initiated by J. Bienacel, in the article entitled “Développement d'un procédé de nitruration plasma des oxydes de grille pour le noeud technologique 65 nm>>, PhD thesis, Université de Marseille, 2005. This XPS measurement gives an integrated dose for a given and already known element distribution in the film, which has to be calibrated beforehand. This technique is routinely used for nitrogen dose measurement of thin gate oxynitride (65/45 nm CMOS thin gate oxides with thicknesses of 15 to 30 Å for example). However, one has to note that the photoelectron escape length is in the order of 40-50 Å, which prevents the use of this tool for interface nitridation in 100 Å thick films (e.g. tunnel oxide). Some XPS tools include an argon sputtering feature that can provide access to the depth of the material. However, such tools are subject to the same kind of measurement errors as all sputtering techniques, such as SIMS.
Thus although the nitrogen characteristics in gate oxide dielectrics are of paramount importance for device operation and reliability as described in the relevant pages of the book by T. Hori, entitled “Gate Dielectrics and MOS ULSIs”, Springer Series in Electronics and Photonics, vol. 34, Springer-Verlag, Berlin, 1997, none of the available clean-room inline techniques can provide access to this information.
It is accordingly desirable to develop a fast, accurate, and in-line characterization technique for use in particular in the characterization of the nitrogen profile in gate oxynitride films.